1. Field of the Invention
The present invention relates to a method of forming a photoresist pattern. The photoresist pattern is specifically used for manufacturing semiconductor devices with a submicrometer resolution.
2. Description of the Prior Art
In the semiconductor technical field, there is a growing need for a higher integration of semiconductor devices. Accordingly, there is a severe technical demand for the production of fine photoresist patterns. One of the fine processing methods employs ionization radiation such as electron beams, X-rays, shortwavelength ultraviolet radiation, and the like, so as to form the photoresist pattern, and thereafter precisely transferring the photoresist pattern onto underlying layers, e.g., substrates by a dry-etching treatment in which ions or a plasma has been filled.
As a transfer apparatus for forming a photoresist pattern for a fine process, an optical reduction type transfer apparatus (aligner) has been mainly used because of its properties of high resolution and high accuracy for alignment. As a light source for this type of transfer apparatus, a g-line emitted from a mercury vaper lamp and being in a region, of near ultraviolet region is most expected in view of its lower absorption in the optical system and higher light outputs.
However, as a positive type photoresist for photolithography using the near ultraviolet radiation, a photoresist is used which is obtained by mixing a novolak resin and a naphthoquinone diazide of a photosensitive material due to its high resolution and dry etching resistance. Further, as a negative type photoresist, a photoresist obtained by mixing a polyvinyl phenol and a bisazide is used. This resist has high sensitivity at the i-line (365 nm).
However, because light of a g-line (436 nm) is most expected as a light source for the optical reduction type transfer apparatus, the sensitivity of resins above the negative type photoresist is low. Further, the positive type photoresists pose difficulties in maintaining a good line width control over the topography because of the reflective notching caused by reflected light from the substrate.
If negative and positive type photoresist patterns can be formed by selecting the proper developing solutions, it is possible to select a method by which a negative or positive type photoresist pattern can be easily obtained in accordance with the photoresist pattern. As a result, various merits are achieved in the manufacture of semiconductor devices.
It is therefore an object of the present invention to provide a method of forming a negative or positive type photoresist pattern by using the proper negative or positive type developing solution and for forming a constant line width pattern even over the substrate topography.